Filter cartridge assemblies, such as those used to filter water in swimming pool and spa applications, are often constructed of a body, which is often cylindrical (although other shapes are also possible). The body comprises a filter medium. To produce the filter cartridge assembly, end-caps are affixed at opposite ends of the body. These end-caps are sometimes affixed to the filter medium by immersing the filter medium into a polyurethane reaction mixture that will harden about the end of the filter medium to form an elastomeric end-cap. The polyurethane reaction mixture is placed in a mold so that, when it hardens, the end-cap has the desired shape. To be suitable as a filter end-cap, especially for filters used in swimming pool and spa applications, the resulting polyurethane elastomer should have excellent impact resistance, tear strength, suitable hardness, sometimes exhibiting a Shore D hardness of at least about 80, and be resistant to chemicals to which the filter cartridge assembly will be exposed.
One of the drawbacks of the foregoing molding process to produce such filter cartridge assemblies is that external mold release agents are used to produce the assembly. This mold release agent, typically a silicone material, is applied to the mold so that the filter cartridge assembly can be removed from the mold relatively easily and with little or no damage to the end-cap. The external mold release agent, however, is, depending on the shape of the mold, either wiped on the mold or sprayed onto the mold to access harder to reach areas. These processes are labor intensive and, in the case of spray application of the mold release agent, undesirable due to the presence of solvents in the silicone spray. Internal mold release agents in a polyurethane reaction mixture can, however, reduce the reactivity of the reaction mixture and increase the time it takes for the polyurethane elastomer to achieve a green strength sufficient for the end-cap to be demolded without damage, thereby reducing productivity.
As a result, it would be desirable to provide processes for producing molded polyurethane elastomers that can be an end-cap of a filter cartridge assembly utilizing isocyanates with an internal mold release agent, thereby eliminating the need to apply an external mold release agent to the mold prior to production of each, or nearly each, filter end-cap. It would be desirable that such processes still provide a filter end-cap exhibiting required physical properties, such as hardness sufficient for use with filters used in swimming pool and spa applications, all without negatively impacting manufacturing productivity.